The present invention relates to that field of the art where milk is converted to coagulated milk products such as cottage cheese by the addition of chemicals rather than the use of natural bacteriological cultures. The greatest obstacle has been the inability to incorporate the acid into the milk without the premature coagulation of the milk precipitation of the casein. In fact, every commercial process for making cottage cheese by the direct acidification of the milk is based on the principle of acidifying the milk at refrigeration temperature (40.degree.F) and subsequently warming the milk. The attempts to acidify milk for cottage cheese at a temperature of 70.degree. are legion, and all of them have been failures.
Fresh fluid milk can be acidified by direct addition of acid to a pH of about 4.50 or above at a temperature of about 40.degree.F without any significant tendency for the milk to coagulate, or for the casein to precipitate or flocculate. Furthermore, it is possible to subsequently warm the acidified milk to a temperature of 70.degree.-80.degree.F without any significant tendency of the milk to coagulate or the casein to precipitate.
The above principle is the basis of several patented processes for the direct acidification of milk in the manufacture of cottage cheese or Baker's cheese. While this principle, and the processes based on it, have made a considerable contribution to the elimination of uncontrollable variations and the resulting loss of product quality (and even complete product loss), there are still some very serious shortcomings in the above principle of acidifying milk by the direct addition of acid.
First, most cottage cheese manufacturers who use natural culturing to acidify the milk do so at a temperature near 90.degree.F. Therefore if such a manufacturer wanted to convert to a prior art direct acidification technique he must provide means for cooling the milk to 40.degree.F and means for warming the acidified milk to about 70.degree.F in the vat. The expense of equipment to cool large volumes of milk is a large capital expenditure.
In addition, the normal vat used for processing is an inefficient heat exchanger and many of the time saving advantages of direct acidification are obviated by the time consuming process of cooling the milk down to 40.degree.F and then heating it back up to 70.degree.F after the acidification. This time may amount to several hours for large vats and that may exceed the time saved by the direct acidification process.
Furthermore, the rate of heating of the milk from 40.degree. to 70.degree.F must be carefully controlled so as to prevent the impairment of product quality and an operator error may render the entire batch unsuitable for its intended use.
The present invention eliminates the necessity for the cooling of milk down to 40.degree.F for the acidification process and the necessary heating of the milk back to the coagulating temperature by spraying the liquid acid directly into the milk at a temperature of from 60.degree. to 90.degree.F at a location where the milk is moving and mixing with the surrounding milk at high velocity.
This eliminates the equipment, energy and time problems inherent in other direct acidification techniques and significantly improves the economics of the entire process.